Some tweaks to the abstract

Try to make things more focused on "security" and not just "encryption".

Reiterate that OS is a pattern, not a protocol itself.

Note that the incremental adoption approach should permit raising
the floor of permissible security levels once broad adoption is attained.
Minor tweaks to the introduction

Make some things explicit for clarity, do not include the subjective
claim that there are too many CAs in the web PKI, minor grammar fixes.